The present invention generally relates to structural members adapted to reinforce a product. The present invention also relates to methods of utilizing the structural member to form reinforced products.
Traditional structures and products experience deterioration or failures of various kinds which create a need for reinforcement. For example, roadways consisting of asphaltic concrete materials experience deterioration and failure over time in the form of reflective cracking, rutting, rolling up at traffic lights and xe2x80x9cpotholes.xe2x80x9d This deterioration and failure of asphaltic concrete roadways require costly, frequent, and time consuming repairs. Another family of products, concrete structures, such as columns, flat slabs, or constant cross-section shapes, deteriorate over time or as a result of seismic activity or need reinforcement for improved properties such as tensile strength. Various approaches have been investigated to address these problems by reinforcing the initial or existing products.
In regards to roadways, asphalt roadways are widely used, yet experience frequent and costly types of deterioration. Asphalt paving consists of an asphalt compound combined with xe2x80x9crock aggregate.xe2x80x9d The aggregate adds to the compression strength of the asphalt with the asphalt compound acting as a matrix to bind the road together. Asphalt roads deteriorate more quickly than concrete roads, and typical forms of deterioration are xe2x80x9creflective crackingxe2x80x9d, curling of the asphalt at places like stoplights, grooving of the asphalt due to repeated vehicular traffic following the same path down the roadway and other cracking of the asphalt surface. xe2x80x9cReflective crackingxe2x80x9d is a major problem in asphalt overlays of existing concrete roads or other road foundations. Reflective cracking occurs where cracks in the existing concrete or asphaltic road or foundation propagate from the existing road up through the new asphalt overlay. This requires costly repairs to otherwise new roads and attacks the strength of the new overlay.
A variety of materials have been tried in the past to attempt to provide reinforcement or stabilization for asphalt roadways. Several products currently seek to address the reflective cracking problem. One product is a non-woven overlay fabric or mat between a concrete road and an asphalt overlay called Petromat(copyright) from Amoco Fabrics and Fibers. Petromat(copyright) uses a random orientation of polypropylene fibers in a fabric mat that is laid down as a barrier between a road or road foundation and an asphalt overlay. The polypropylene does not have the modulus to resist expansion of concrete road in attempting to address the problem of reflective cracking. Also, the mat is of tight construction and does not allow asphalt or concrete to pass through the structure, instead acting as a barrier between the layers. The mat is therefore not incorporated as a reinforcement structure throughout the new overlay. Instead, the mat acts only as a barrier which can wrinkle or fold in application. Further, a leveling or filling of cracks is necessary before using the Petromat(copyright).
Others have tried to use mesh structures of plastic materials and woven fabrics to reinforce roadways. One product, Glasgrid(copyright) is a woven (leno) glass fiber fabric grid, coated with asphalt black coating with one side having self-adhesive properties. Another product, Raupave(copyright) is a geogrid composed of high-tenacity fiberglass yarn which is woven into a uniform, leno grid configuration. Another product, Polyfelt PGM-G(copyright) consists of fiberglass rovings laid in a grid pattern onto a non-woven felt with the felt meant to act as a water barrier to attempt to retard reflective cracking.
Attempts have been made to use other tightly constructed structures which reinforce the roadway, but do not allow the passage of asphaltic concrete road materials through the reinforcing structure in the normal paving process. Difficulties have arisen from using such tightly constructed reinforcement members in road construction. These tightly constructed reinforcement members create a barrier between the new road overlay and the old road or foundation restricting the passage through or incorporation of asphaltic concrete materials into the reinforcement member. This reduces the reinforcement benefits of the reinforcing member and enables slippage or movement in the normal paving process.
Another family of products and structures which require reinforcement are concrete structures and other masonry or cementitious materials. These concrete materials have low tensile strength yet have good compressive strength. When using concrete as a structural member, for example, in a bridge, building or the like, reinforcement is often used to impart the necessary tensile strength. In new and existing concrete structures, such as precast driveways, slabs, sidewalks, pipe etc, reinforcement has been undertaken with a variety of steel shapes such as open steel meshes, steel rebar, and steel grids. Steel grids have been used in reinforcing concrete structures such as decking for drawbridges. These steel grids are a closed cell structure, and each section of steel grid contains and confines a rectangular or square column of concrete. These types of grids are inherently very inefficient in their use of the reinforcing material.
Steel and other metals used as a reinforcing agent are subject to corrosion. The products of corrosion result in an expansion of the column of the steel which causes a xe2x80x9cspallingxe2x80x9d effect which can cause a breakup and deterioration of the concrete structure. This breaking and crumbling of concrete structures are severe in areas of high humidity and areas where salt is used frequently on roads, driveways and sidewalks to melt ice or snow. Bridges over waterways in areas such as the Florida coast or Florida Keys are exposed to ocean air which causes deterioration and a short lifespan requiring constant rebuilding of these bridges. Concrete structures in the Middle East use concrete made with the local acidic sand which also causes corrosion of steel reinforcements.
To replace traditional steel in reinforcing concrete, many types of plastics have been considered. One attempted replacement for steel in reinforcement uses steel rebars coated with epoxy resin. Complete coating coverage of the steel with epoxy, however, is difficult. Also, due to the harsh handling conditions in the field, the surface of the epoxy coated steel rebars frequently will be nicked. This nicking results in the promotion of localized, aggressive corrosion of the steel and results in the same problems as described above.
Fiberglass composite rebars have been used in reinforcing concrete structures such as the walls and floors of x-ray rooms in hospitals where metallic forms of reinforcement are not permitted. The method of use is similar to steel rebars. The fiberglass composite rebars have longitudinal discrete forms which are configured into matrixes using manual labor. Concrete is then poured onto this matrix structure arrangement.
Fiberglass composite rebars are similar to steel rebars in that the surface is deformed. Fiberglass gratings which are similar to steel walkway gratings also have been used as reinforcements in Concretes, but their construction, which forms solid walls, does not allow the free movement of matrix material. This is due to the fact that the xe2x80x9cZxe2x80x9d axis or vertical axis reinforcements form solid walls.
In dealing with reinforcing concrete support columns or structures, wraps have been applied around the columns to act like girdles and prevent the concrete from expanding and crumbling. Concrete is not a ductile material, thus, this type of reinforcing is for only the external portion of the column. One type of wrap consists of wrapping a fabric impregnated with a liquid thermosetting resin around the columns. The typical construction of these wraps has glass fiber in the hoop direction of the column and glass and Kevlar fibers in the column length direction. Another approach uses carbon fiber uni-directional (hoop direction) impregnated strips or strands which are designed to be wound under tension around deteriorated columns. The resulting composite is cured in place using an external heat source. In these approaches the materials used in the reinforcing wraps are essentially applied to the concrete column in an uncured state, although a prepreg substrate may be employed which is in a xe2x80x9csemi-curedxe2x80x9d state, i.e. cured to the B-stage. When using a woven fabric, xe2x80x9ckinkingxe2x80x9d can take place when using either carbon or glass fibers, because the weaving process induces inherent xe2x80x9ckinksxe2x80x9d in either a woven wet laminate or woven prepreg, which results in a less than perfectly straight fiber being wrapped around the column.
Another approach to reinforcing concrete structures and columns is to weld steel plates around the concrete columns to give support to the concrete wall. Such steel plates are also subject to corrosion and loosening resulting from deterioration of the column being supported. This approach is only an external reinforcement and lacks an acceptable aesthetic appearance which makes it undesirable.
An approach to reinforcing concrete mixes has been using short (xc2xc to 1xe2x80x3) steel, nylon or polypropylene fibers. Bare xe2x80x9cE-typexe2x80x9d glass fibers are generally not used due to the susceptibility of glass fibers to alkaline attack in Portland cement.
Thus, there is a need for improved structural members adapted to reinforce a variety of products. For example, there is a need for an improved structural reinforcement member for use in asphaltic concrete roadways. Additionally, there continues to be a need for a structural reinforcement member for concrete structures which accomplishes the reinforcement or increases material properties of the concrete structure without being subject to corrosion or attack. There also remains a need for methods to reinforce products using these structural members.
It is an object of the invention to overcome the deficiencies of the prior art as noted. A more particular object of this invention is to provide a structural member adapted to effectively reinforce a variety of different products. A further object of the invention is to provide methods for utilizing the structural member adapted to reinforce a product, and for efficiently producing the structural member.
The above and other objects and advantages of the present invention are achieved by the provision of a structural member adapted to reinforce a product and methods for utilizing the same as described herein. One embodiment of the invention comprises a gridwork comprising a set of warp strands and a set of weft strands disposed at substantially right angles to each other, with each of the strands comprising at least one continuous filament, and with at least some of the strands of each set being spaced apart so as to define an open structure, and with the gridwork being impregnated substantially throughout with a thermosettable B-stage resin so as to interlock the strands at their crossover points and maintain the gridwork in a semi-flexible state which permits the gridwork to conform to the shape of the product to be reinforced. Thus with the gridwork in a semi-flexible state, the member can be conformed to the shape of the product to be reinforced. The resin is curable in situ in the product to form a rigid composite by heating to a predetermined temperature. The product is thereby reinforced with the cured member within it.
Preferably, the sets of strands are non-interlaced, and in one embodiment, the set of warp strands and the set of weft strands are substantially linear, so that the gridwork is generally flat. In another embodiment, the set of warp strands is corrugated into alternating ridges and grooves, and wherein the set of weft strands is substantially linear, so that the gridwork has a three-dimensional configuration.
Still another embodiment of the invention comprises a structural member of the structure defined above, but which is instead impregnated substantially throughout with a fully cured thermoset resin so as to interlock the strands at their crossover points and maintain the gridwork in a relatively rigid state. This embodiment is particularly suitable for use in reinforcing products made of Portland cement concrete.
Another embodiment of the invention comprises a three-dimensional structural reinforcement member comprising a three-dimensional open mesh gridwork as described used in conjunction with a generally flat open gridwork as described with the generally flat gridwork being positioned to be coextensive with one of the planes of the three-dimensional gridwork. One particular embodiment of the invention comprises this three-dimensional structural reinforcement member impregnated substantially throughout with a thermosettable B-state resin as described previously so as to interlock the strands at their crossover points and to retain the gridworks in a semi-rigid three-dimensional configuration. Another particular embodiment of the invention comprises this three-dimensional structural reinforcement member impregnated with a fully cured thermoset resin so as to interlock the strands at their crossover points and maintain the gridwork in a relatively rigid state.
Another embodiment of the invention comprises a method of structurally reinforcing a product comprising the steps of providing an open mesh gridwork as described above being impregnated substantially throughout with a thermosettable B-stage resin so as to interlock the strands at their crossover points and maintain the gridwork in a semi-flexible state which permits the gridwork to conform to the shape of the product to be reinforced; applying the gridwork to the product; and then applying heat to the gridwork so as to cure the resin and convert the same into a cured composite to thereby rigidize the gridwork and reinforce the product.
A further embodiment of the invention comprises a method of fabricating a reinforced roadway composed of an asphaltic concrete material comprising the steps of preparing a foundation for the roadway; providing an open mesh gridwork as described above impregnated substantially throughout with a thermosettable B-stage resin so as to interlock the strands at their crossover points and maintain the gridwork in a semi-flexible state. Asphaltic concrete, which is heated to a predetermined temperature is then applied upon the foundation, with the gridwork embedded therein, and such that the heat of the asphaltic concrete acts to cure the resin in situ and convert the same into a cured composite to thereby rigidize the gridwork and reinforce the asphaltic concrete.
Still another feature of the present invention involves an efficient method of producing a structural member of the described type, and which includes the steps of advancing the gridwork along a path of travel while
(1) immersing the advancing gridwork in a liquid resin which is thermosettable and capable of being heated to cure to the B-stage,
(2) guiding the resin coated advancing gridwork through a nip so as to squeeze off excess resin, cause the resin to penetrate into the strands, and firmly press the crossover points of the sets of strands together, and then
(3) heating the advancing gridwork to an extent sufficient to cause the resin to cure to the B-stage without fully thermosetting.
The resulting gridwork with the B-stage resin may then be formed into a supply package, such as a supply roll, so that it may be conveniently transported to the job site. At the job site, the gridwork is withdrawn from the supply package, conformingly applied to the product, and then heated so as to cure the resin and convert the same into a cured composite and thereby rigidize the gridwork and reinforce the product. Where the gridwork is used to reinforce asphaltic concrete which is applied to the roadway foundation in a heated condition, the heat of the asphaltic concrete acts to cure the resin, as described above.